Switch position supervising device

ABSTRACT

A device for the electronic supervision of a number of switching devices, each of which is connected to one side of a load, the other side of the loads being connected to a further switching device which is constructed as a controlled rectifier. After a starting pulse, the controlled rectifier receives an extinguishing pulse of a given value which can bring the controlled rectifier to the non-conducting state only if the current flowing through the rectifier due to the non-conducting state of all other switching devices has reached a given minimum value. If at least one of the said number of switching devices has remained conducting, the controlled rectifier continues to carry current, said current being detected, thus causing an alarm.

United States Patent 1191 van Kempen et al.

1451 Feb. 20, 1973 SWITCH POSITION SUPERVISING DEVICE [75] Inventors: Dick van Kempen; Hans Spaargarcn, both of Rijswijk, Netherlands [73] Assignee: U.S. Philips Corporation, New

York,N.Y.

[22] Filed: Oct. 19, 1971 [21] Appl. No.: 190,579

' [30] Foreign Application Priority Data 1 Primary Examiner-Donald J. Yulsko Assistant Examiner-Daniel Myer Att0rneyFrank R. Trifari [57] ABSTRACT A device for the electronic supervision of a number of switching devices, each of which is connected to one 01:1.22, 1970 Netherlands ..70l5436 side of a the Side of wads being nected to a further switching device which is con- 52 US. (:1. ..340/2s3 R, 340/282 meted as a controlled mime" After a Starting 5 1 Int. Cl. ..G08h 21/00, H03k 17/72 Pulse, the controlled rectifier receives an extinguishing 58 Field of Search ..340/24& R, 253 R, 252, 256, Pulse of a given value which can bring the controlled 340 232 rectifier to the non-conducting state only if the current flowing through the rectifier due to the non-con- [56] Ref Cited ducting state of all other switching devices has reached a given minimum value. If at least one of the UNITED STATES PATENTS said number of switching devices has remained con- 1,931,862 10/1933 Felten ..340/248R ducting, the controlled rectifier continues to carry 2,129,143 9/1938 Lamb ..340/248 R X current, said current being detected, thus causing an 2,459,186 1/1949 Sherman ..340/253 R X alarm. 2,701,965 2/1955 Sherman ..340/248 R X 3,215,996 11/1965 Schwartz et a1. ..340/256 X 2 Claims, 2 Drawing Figures STARTING EXTINGUISHING PULSE PULSE SOURCE SOURCE S1 B1 (T C1 I y 1 2 PULSE S2 SHAPER Kzo--/- FLIP FLOP device is opened.

In apparatus in which a number of loads is continuously switched on and off, use is often made of arrangements in which on the one side a first, a second etc. load are individually connected to a first, a second etc. switching device, respectively, and on the other side the loads are connected collectively, or divided in groups, to a said further switching device. A line printer is an example of such an apparatus. The loads to be switched therein are coils for energizing printing mallets which are thus moved to a character roller. The said further switching device serves to connect the coils, to a supply source during a given period (printing cycle), whilst the said first, second etc. switching device can be closed at given instants, dependent of the position of the character roller, for a short period within the printing cycle so as to enable current to flow through the relevant coils, thus enabling a printing stroke. If the further switching device is no longer conducting after a duty cycle in such apparatus, none of the coils can carry current any longer. If one of the first, second etc. switching devices were not to return to the non-conducting state after having been conducting, the relevant load would carry current again each subsequent duty cycle. This leads to errors in the duty cycle and, moreover, the load is liable to be destroyed (burning out of a coil, for example) consequently, in apparatus of this kind it is necessary to be sure that after completion of a duty cycle, all first, second etc.

switching devices return to their rest or non-conducting state.

The invention has for its object to provide a device by which this can be unambiguously established. To this end the device according to the invention is characterized in that the further switching device is a controlled rectifier which, after having been rendered conducting by a starting pulse, can be rendered noncon'ducting by an extinguishing pulse of a given value only if the current flowing through the controlled rectifier due to the non-conducting state of said at least first switching device has a given minimum value, a detector being provided in which, in the case that after said extinguishing pulse the controlled rectifier remains conducting due to the conducting state of a said at least first switching device, the current flowing through the controlled rectifier can be detected for an alarm. By using the controlled rectifier according to the invention, it is possible to maintain a current, capable of occurring due to the failure to become non-conducting of one of the first, second etc. switching devices, through I the controlled rectifier, so that it can be detected.

Because the duty cycles follow each other in rapid succession in said apparatus, it is desirable to be able to establish the failure of such a first, second etc. switching device to become non-conducting within a given period of time after the extinguishing pulse for the controlled rectifier has appeared. For this purpose, the device according to the invention can be provided with a simple logic circuit: a pulse shaper in which the extinguishing pulse can generate a time pulse of given duration, the detector being extended with a memory circuit which can be set by said time pulse and which can be reset by the change-over from the conducting to the non-conducting state of the controlled rectifier when said minimum value of the current flowing through the controlled rectifier is reached, the output of the memory circuit and a terminal to which the inverse of said time pulse is applied being connected to an AND-function gate, said ANd-function gate supplying an alarm signal only if the memory circuit is not reset during the time pulse.

In order that the invention may be readily be carried into effect, one embodiment thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawing, in which:

FIG. 1 shows a diagram of a possible embodiment of a device according to the invention, and

FIG. 2 shows a time diagram of the operation of the device shown in FIG. 1.

The references B,, B,,, B,, in FIG. 1 denote coils representing loads, such as used, for example, in the example of the line printer. A first, second etc, switching device is denoted by 8,, S B,,, respectively. The later may be electronic switches which become conducting when signals k,, K, I(,, appear. These signals K,, K, K, represent the control commands for a line printer which indicate which printing mallet is to be energized at which instant. The group of switching devices 8,, S S, is connected to a voltage source terminal V, via a controlled rectifier CR (e.g. a thyristor). A starting pulse source 1 is provided which supplies a starting pulse St in reaction to a command C,. An extinguishing pulse source 2 is provided which supplies an extinguishing pulse Df in reaction to a command C,. These pulses St and Df are applied to a gate electrode G of the controlled rectifier CR. The cathode K of the controlled rectifier CR is not only connected to the group of switching devices 8,, S, S,,, but also to an impedanceZ (e.g. a resistor). The voltage state on the cathode K is compared in a threshold device 3 with a threshold voltage on a terminal V The reference numeral 4 denotes a pulse shaper which, driven by an extinguishing pulse from 2, supplies a time pulse f having a given duration r on line B. A memory circuit is formed by a flipflop FF, the output FFl of which is connected to an input of an AND-function gate 5. GAte 5 also receives the inverse of the said time pulse B (circle on input). Output A, carries a voltage if alarm is given according to the invention.

The operation can be readily described with reference to the time diagram shown in FIG. 2.

When a starting pulse ST, appears, the controlled rectifier CR opens and the impedance Z enables current to flow. The resultant current I has a value I,, which is the hold current for the controlled rectifier increased by the leakage currents capable of occurring in the circuit of the group of switching devices 8,, S, 8,. Each time that the one of the switching devices 8,, S, S, closes, a large current I, arises through one of the coils B,, B, B,,, by which a printing mallet is energized. If a plurality of mallets is simultaneously energized, the current I increases to a value of, for example, I,. The currents I I, flow only as long as one or more switching devices are conducting: time A t. After a time T after the starting pulse St an extinguishing pulse Df appears: a duty cycle has been completed. In practice it will occur that after the end of a duty cycle the extinguishing pulse is not immediately given, but only after a delay. This is due to the fact that, for example, in the case of line printers, it is better to wait until the mallets have returned to their rest position. This is because of counter voltages in the coils caused by the returning of the mallets. This extinguishing pulse attemps to bring the controlled rectifier to the non-conducting state. The extinguishing pulses Df have such a value (amplitude) that this is successful only if a current having the value I, flows, i.e. a given minimum quiescent current. This current I is present only if all switching devices have meanwhile reached the nonconducting state. When the controlled rectifier becomes non-conducting, the voltage value U of the voltage on the cathode X will start to decrease. When the voltage on the cathode becomes equal to or less than the voltage V,, respectively, the threshold value of the device 3, the voltage A 1 appears on the output of 3. A for as long as the voltage U on the cathode K exceeds the value 2. When an extinguishing pulse Dfl appears, this pulse is used to generate a time pulse B in pulse shaper 4. This pulse B has a fixed duration of 1- time units. r indicates the time within which the change-over from A 0 to A i has to occur, so as to signify that the controlled rectifier has changed from the conducting to the non-conducting state.

The leading edge of the pulse B sets the flipflop FF to its l-state i.e. the output FFl then carries l-signal. The flip-flop FF can be reset only by the change-over from A 0 to A 1. In this case (FIG. 2) FF] =1 only during a short period :1. The AND-function gate then always applies a O-signal to A1, i.e. no alarm occurs.

Assume that after a period t another duty cycle starts. A starting pulse St, is present, the controlled rectifier carries current (A 0 again), and switching devices open and close (I,, I It appears that one of the switching devices S S S does not become non-conducting (continuously traced I, in FIG. 2i). If the further circuit CR were not'a controlled rectifier according to the invention, this failure to become nonconducting would not be noticed. By using the provided controlled rectifier CR the following takes place: the extinguishing pulse Df2 is not capable of rendering CR non-conducting, as I, I This means that current continues to flow after this extinguishing pulse DF This is detected by the fact that A O prevails after the appearance of Df2. This can be readily established in a logical manner by means of the configuration comprising the flipflop FF and the AND-function gate 5. This is because during the duration of pulse B, leading edge of which set the flipflop FF to the l-state, non changeover from A 0 to A 1 occurs, so that FF is not reset. This means that the output FFl carries a l-signal, also after the pulse B has ended. AND-function gate 5 receives l-signal on both inputs (as F 1, when B 0), so that the output Al supplies l-signal i.e. an alarm signal. By means of this signal an intervention in the apparatus can be introduced. For example, the result may be that the starting pulse source does not receive a new command C for generating a starting pulse St (St is canceled) and, in addition, the supply will be entirely disconnected by the removal of V so that I becomes zero and the load is not damaged.

WHAT IS CLAIMED IS:

1. A device for the electronic supervision of at least one first switching device which is connected to one side of a load, the other side of said load being connected to a further switching device for connecting a supply source, the at least first switching device having to be open when the further switching device is opened, characterized in that the further switching device is a controlled rectifier (CR) which, after having been rendered conducting by a starting pulse (St), can be rendered non-conducting by an extinguishing pulse (Df) of a given value only if the current (I) flowing through the controlled rectifier (CR) due to the fact that said at least first switching device (8,, S, 8,.) is non-conducting has a given minimum value (I a detector (3) being provided in which, in the case that after said extinguishing pulse (Df) the controlled rectifier (CR) remains conducting due to the conducting state of a said at least first switching device (8,, S, S,,), the current (I 1 flowing through the controlled rectifier (CR) can be detected for an alarm (A remains zero).

2. A device as claimed in claim 1, characterized in that a pulse shaper (4) is provided in which a time pulse (B) of a given duration (1') can be generated by the extinguishing pulse (Df), the detector (3)being extended with a memory circuit (FF) which can be set by said time pulse (B) and which can be reset by the change-over from the conducting to the non-conducting state of the controlled rectifier (CR) when said minimum value of the current (I) flowing through the controlled rectifier is reached, the output (FF of the memory circuit (FF) and a terminal to which the inverse of the said time pulse is applied being connected to an AND-function gate (5), said AND-function gate (5) supplying an alarm signal (Al) only if the memory circuit (FF) is not reset during said time pulse (B). 

1. A device for the electronic supervision of at least one first switching device which is connected to one side of a load, the other side of said load being connected to a further switching device for connecting a supply source, the at least first switching device having to be open when the further switching device is opened, characterized in that the further switching device is a controlled rectifier (CR) which, after having been rendered conducting by a starting pulse (St), can be rendered non-conducting by an extinguishing pulse (Df) of a given value only if the current (I) flowing through the controlled rectifier (CR) due to the fact that said at least first switching device (S1, S2 . . . Sn) is non-conducting has a given minimum value (I1), a detector (3) being provided in which, in the case that after said extinguishing pulse (Df) the controlled rectifier (CR) remains conducting due to the conducting state of a said at least first switching device (S1, S2 . . . Sn), the current (I2, I3) flowing through the controlled rectifier (CR) can be detected for an alarm (A remains zero).
 1. A device for the electronic supervision of at least one first switching device which is connected to one side of a load, the other side of said load being connected to a further switching device for connecting a supply source, the at least first switching device having to be open when the further switching device is opened, characterized in that the further switching device is a controlled rectifier (CR) which, after having been rendered conducting by a starting pulse (St), can be rendered non-conducting by an extinguishing pulse (Df) of a given value only if the current (I) flowing through the controlled rectifier (CR) due to the fact that said at least first switching device (S1, S2 . . . Sn) is non-conducting has a given minimum value (I1), a detector (3) being provided in which, in the case that after said extinguishing pulse (Df) the controlled rectifier (CR) remains conducting due to the conducting state of a said at least first switching device (S1, S2 . . . Sn), the current (I2, I3) flowing through the controlled rectifier (CR) can be detected for an alarm (A remains zero). 